1. Field of the Invention
The present invention relates to a voltage generating circuit, a data driver, and a display unit.
2. Related Art
As a liquid crystal panel (electro-optical device) used in electronic equipment such as a mobile phone, there are conventionally known a liquid crystal panel of a simple matrix method and a liquid crystal panel of an active matrix method using a switching element such as a thin film transistor (hereinafter abbreviated as TFT).
The simple matrix method has an advantage of being easy to produce low power consumption as compared to the active matrix method, while its disadvantage is its difficulty to produce multi-color and display animation. On the other hand, the active matrix method has an advantage of being suited to multi-color production and animation display, while it has a disadvantage of its difficulty to produce low power consumption.
And demands for multi-color production and animation display are intensifying in recent years with respect to mobile electronic equipment such as a mobile phone so s to provide high quality images. Consequently, in lieu of the liquid crystal panel of the simple matrix method, the liquid crystal panel of the active matrix method is being used now.
Now, in the liquid crystal panel of the active matrix method, it is desirable to set up an operational amplifier functioning as an output buffer inside a data driver which drives a data line of the liquid crystal panel. The operational amplifier has a high driving capacity capable of supplying voltage stably to the data line.
By the way, as multiple gray scales continue to obtain high quality of displayed images, it becomes necessary to increase the number of gray scale levels. In this case, a gray scale voltage corresponding to a gray scale value must be generated within a preset range of voltage.
However, the operational amplifier drives the data line based on the gray scale voltage corresponding to the gray scale value. As a result, it is possible to prevent quality of display from deteriorating by supplying a generated gray scale voltage to an arithmetic amplifier without lowering it.
For example, in the data driver, it is designed such that a DAC (voltage generating circuit in a broad sense) selectively outputs the gray scale voltage corresponding to the gray scale value out of a plurality of gray scale voltages. Accordingly, it is desirable that a path through which the gray scale voltage outputted by the DAC passes be of low impedance.
The present invention has been made in view of the above-mentioned technical problem, and it is an object thereof to provide a voltage generating circuit, a data driver, and a display unit which can output a generated voltage corresponding to digital data while suppressing a voltage drop thereof out of the plurality of generated voltages.